The overall object of the proposed research is to determine the biological significance of the various components of the immune response against primary tumors. The system chosen for study is that of primary fibrosarcomas induced in inbred mice by neonatal injection of Rous sarcoma virus (RSV). The specific objectives of this work are to determine which specific cells are responsible for the difference which exists between the anti-tumor response of mice which develop primary Rous sarcomas and that of similar exposed litter mates which do not, and to define the difference in the immune response to Rous sarcoma specific antigen(s) between a strain relatively susceptible to primary oncogenesis (C57BL/10) and one relatively resistant (B10.D2). These experiments will also lead to a direct test of the hypothesis of immune surveillance against neoplasia. These objectives will be approached by transferring defined cell populations of lymphoid cells or serum from various types of donor mice to syngeneic recipients which have been infected with Rous sarcoma virus, a known proportion of which can be predicted to develop tumors, and by use of the Winn assay. The donor mice will include: 1) primary tumor hosts and their similarly infected, but tumor-free litter mates; and normal adult syngeneic mice.